Front referenced anode

ABSTRACT

Apparatus and methods for electroplating are described. Apparatus described herein include anode supports including positioning mechanisms that maintain a consistent distance between the surface of the wafer and the surface of a consumable anode during plating. Greater uniformity control is achieved.

FIELD OF INVENTION

The invention relates generally to electroplating apparatus, moreparticularly improved anodes and anode assemblies and methods ofelectroplating a metal onto a work piece.

BACKGROUND

Electroplating uses electrical current to reduce cations of a desiredmaterial from a solution and coat a conductive object, the work piece,with a thin layer of the material, such as a metal. In a typicalelectroplating cell, the part to be plated is the cathode and the anodeis made of the metal to be plated on the part. Both components areimmersed in an electrolyte containing one or more dissolved metal saltsas well as other ions that permit the flow of electricity through theelectrolyte. Metal atoms of the anode are oxidized to ions, allowingthem to dissolve in the electrolyte. In this manner, the ions in theelectrolyte bath are continuously replenished by the anode. At thecathode, the dissolved metal ions in the electrolyte solution arereduced at the surface of the cathode, such that they “plate out” ontothe cathode.

The above described method of plating uses a “consumable” anode, thatis, during plating the anode is dissolved into the electrolyte andeventually is consumed and must be replaced in order to electroplatefurther. As the anode is consumed, it undergoes shape change duringplating. This shape change can have detrimental effects on platinguniformity because the change in shape of the anode creates a change inthe plating conditions. For example, the electric field shape anddensity between the work piece and the anode changes during plating dueto the change in distance between the work piece and the anode due tothe anode's consumption. In certain plating applications, for exampleelectroplating a metal onto a semiconductor wafer, it is important tohave highly uniform plating onto the semiconductor wafer. When platinglayers that are very thin, on the order of angstroms or microns thick,and where uniformity is critical, even small changes in the anode'sshape can create non-uniformities in the plated metal.

SUMMARY OF INVENTION

Apparatus and methods for electroplating are described. Apparatusdescribed herein include anode supports including positioning mechanismsthat maintain a consistent distance between the surface of the wafer andthe surface of a consumable anode during plating. Greater uniformitycontrol is achieved.

One embodiment is an electroplating apparatus, including: (a) a workpiece holder for holding a work piece in place during electroplating;and (b) an anode support comprising an anode positioning mechanism foradjusting the position of a consumable anode to provide a consistentdistance between the consumable anode and the work piece over a periodof time during which the consumable anode is consumed. In oneembodiment, the work piece holder is configured to hold a semiconductorwafer. In certain embodiments, the apparatus further includes theconsumable anode, where the consumable anode includes a substantiallyplanar surface that is substantially parallel to the plating surface ofthe semiconductor wafer during plating. In some embodiments, thesubstantially planar surface is at least co-extensive with the platingsurface of the semiconductor wafer. The anode may have a unitary body,or in certain embodiments, the consumable anode includes two or moresections that, when registered with each other, form a disk-shapedanode. In one embodiment, the consumable anode includes four circularsectors having equivalent central angles. In certain embodiments, theconsumable anode includes copper, and in one embodiment the consumableanode is copper.

In one embodiment, the anode positioning mechanism includes: (i) asupport plate, for supporting the consumable anode; and (ii) a drivecomponent, configured to apply upward force to the support platesufficient to raise the anode. For example, with a disk shaped anode,the support plate is of sufficient area to support the anode, but neednot be the same diameter as the anode. In one embodiment, the drivecomponent includes one or more springs that are compressed between thesupport plate and a bottom region of a plating chamber and/or a baseplate configured to lie in the bottom region of the plating chamber. Ina specific embodiment, the one or more springs are compressed betweenthe support plate and the base plate. The anode positioning mechanismmay further include one or more hard stops configured to limit thedistance that the consumable anode is pushed by the one or more springsor other drive mechanism and thereby maintain the consistent distancebetween the consumable anode and the work piece over the period of timeduring which the consumable anode is consumed.

In one embodiment, the support plate is annular with a hollow occupiedby a charge plate, the charge plate configured to attach to the bottomof the consumable anode and attach to the base plate via one or morecables or other flexible conductive elements. The cables can be used tosupply electricity to the anode.

Another embodiment is a method of electroplating a metal onto a workpiece, the method including maintaining a consistent distance betweenthe plating surface of the work piece and a surface of a consumableanode during plating, by adjusting the position of the consumable anodeduring plating to compensate for consumption of the surface of theconsumable anode.

These and other features and advantages will be described in furtherdetail below, with reference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description can be more fully understood whenconsidered in conjunction with the drawings in which:

FIG. 1 is a cross section schematic of conventional plating apparatus.

FIG. 2 is a cross section schematic of plating apparatus describedherein.

FIGS. 3A-3C depict various illustrations of anode assemblies describedherein.

FIG. 4 depicts a cross section schematic of anode supports describedherein in relation to plating cells employing one or more components forfield shaping and controlling during plating.

FIGS. 5A-5F depict various illustrations of a plating apparatus.

FIG. 6 depicts aspects of a process flow.

DETAILED DESCRIPTION

When electroplating a metal onto a semiconductor wafer, it is importantto have highly uniform plating onto the semiconductor wafer, especiallywhen plating layers that are very thin, on the order of angstroms ormicrons thick. In this regime, for example, uniformity is critical, andeven small changes in the anode's shape can create non-uniformities inthe plated metal. Conventional plating methods and tools address thischallenge, for example, by manipulating the electrical field and currentdensity by the use of, for example, auxiliary cathodes, field shapingelements and the like, to compensate, at least in part, for the changinggap distance and obligatory power increases that change the resistivityprofile during plating. While these address non-uniformity and stillhold value, it is desirable to avoid the issues associated with changinggap distance between the work piece and consumable anode during plating.

The inventors have found that by maintaining a consistent distancebetween the surface of the wafer and the surface of a consumable anodeduring plating, greater uniformity control is achieved. Other benefitsof maintaining a consistent gap between the consumable anode and thewafer plating surface during plating include: 1) decreasing thesensitivity to resistive variations in the plating cell that occur dueto the change in gap distance from the anode being consumed, 2)decreasing the sensitivity to resistive variations of electrolyte 3)obviating the power increase requirements that are obligatory when thedistance between the cathode and anode increases, that is, a constantvoltage may be applied during plating, 4) obviating the need foroversized power supplies, 5) avoiding early replacement the anode toreestablish a suitable gap between the work piece and the anode, 6)addressing anode passivation issues, and 7) lowering the cost ofownership for the anode and related plating apparatus. Anodes describedherein may be thicker than conventional consumable anodes, and thus muchlonger times can be spanned before an anode needs to be changed. Sincethe gap between the anode surface and the work piece is maintained, forexample within described tolerances, such thicker anodes can be morefully used, rather than sacrificing a large portion of the anode simplybecause an unacceptable variation in resistivity is established in theplating cell between the anode and work piece due to the gap increasingduring plating.

Anodes described herein may have features for registering the anode witha support plate. Anodes may have a singular body or be assembled fromtwo or more pieces to aid in assembling an anode positioning mechanismand attaching the anode to the positioning mechanism. Additionalfeatures that may be included as components of assemblies describedherein include guide rods which register with channels in anodes inorder to aid in assembly and/or function of the positioning mechanism oran anode support, one or more hard stops for maintaining a resistanceagainst a force used to position the consumable anode, so that theconsistent gap is maintained, and configurations that take into accountspace savings so that the assemblies fit into existing plating hardware.

One embodiment is an electroplating apparatus, including: (a) a workpiece holder for holding a work piece in place during electroplating;and (b) an anode support comprising an anode positioning mechanism foradjusting the position of a consumable anode to provide a consistentdistance between the consumable anode and the work piece over a periodof time during which the consumable anode is consumed. In oneembodiment, the work piece holder is configured to hold a semiconductorwafer. In certain embodiments, apparatus further include the consumableanode, where the consumable anode includes a substantially planarsurface that is substantially parallel to the plating surface of thesemiconductor wafer during plating. In some embodiments, thesubstantially planar surface is at least co-extensive with the platingsurface of the semiconductor wafer. The term “at least co-extensive”means that the area of the surface of the anode is at least the same, ifnot greater than, that of the wafer. That is, the wafer “sees” anodesurface at all points on the plating surface. Put another way, there iscomplete overlap of the anode surface being consumed and the platingsurface of the wafer. In other embodiments, the anode's surface facingthe wafer is smaller than that of the plating surface of the wafer. Inone embodiment, for example where the anode has a disk shape, theaforementioned embodiments translate to the anode having the same orlarger diameter than the plating surface of the wafer, or the anodehaving a smaller diameter than the plating surface of the wafer,respectively. The anode may have a unitary body, or in certainembodiments, the consumable anode includes two or more sections that,when registered with each other, form a disk-shaped anode. In oneembodiment, the consumable anode includes four circular sectors havingequivalent central angles. In certain embodiments, the consumable anodeincludes copper, and in one embodiment the consumable anode is copper.

The term “anode assembly” is meant to include an anode, anode support,positioning mechanisms and associated hardware that may be used inand/or be components of an electroplating apparatus. Thus anode assemblydoes not specifically require an assembly of anode segments used to makea consumable anode.

In one embodiment, the anode positioning mechanism includes: (i) asupport plate, for supporting the consumable anode; and (ii) a drivecomponent, configured to apply upward force to the support platesufficient to raise the anode. For example, with a disk shaped anode,the support plate is of sufficient area to support the anode, but neednot be the same diameter as the anode. In one embodiment, the drivecomponent includes one or more springs that are compressed between thesupport plate and a bottom region of a plating chamber and/or a baseplate configured to lie in the bottom region of the plating chamber. Ina specific embodiment, the one or more springs are compressed betweenthe support plate and the base plate. The anode positioning mechanismmay further include one or more hard stops configured to limit thedistance that the consumable anode is pushed by the one or more springsand thereby maintain the consistent distance between the consumableanode and the work piece over the period of time during which theconsumable anode is consumed.

The hard stop may include an annular structure. In one embodiment, thehard stop includes a spoked wheel structure including a plurality offlutes for delivering electrolyte flow onto to the consumable anode. Insuch embodiments, the annular structure, for example the spoked wheelstructure, may include one or more protrusions that rest against theconsumable anode during consumption of the consumable anode and preventthe anode from touching the main body and/or the plurality of flutes ofthe spoked wheel structure.

In one embodiment, the support plate is annular with a hollow occupiedby a charge plate, the charge plate configured to attach to the bottomof the consumable anode and attach to the base plate via one or morecables.

One embodiment is the electroplating apparatus as described above,further including: (i) an ionically resistive ionically permeableelement shaped and configured to be positioned between the work pieceand the consumable anode during electroplating, the ionically resistiveionically permeable element having a flat surface that is substantiallyparallel to and separated from a plating face of the work piece by a gapof about 5 millimeters or less during electroplating; and (ii) anauxiliary cathode located between the consumable anode and the ionicallyresistive ionically permeable element, and peripherally oriented toshape the current distribution from the consumable anode, while theauxiliary cathode is supplied with current during electroplating. In oneembodiment, the ionically resistive ionically permeable element has anionically resistive body with a plurality of non-communicating channelsthrough the body, wherein said plurality of non-communicating channelsallow for transport of ions through the element, and whereinsubstantially all channels have a principal dimension or a diameter ofthe opening on the surface of the element facing the surface of the workpiece of no greater than about 5 millimeters. In one embodiment, theionically resistive ionically permeable element is a disk having betweenabout 6,000-12,000 channels and/or has a porosity of about 5% porous orless. In another embodiment, the ionically resistive ionically permeableelement is a disk having less than 6,000 channels and/or has a porosityof greater than 5%. Electroplating apparatus may further include asecond auxiliary cathode located in substantially the same plane as theplating surface of the work piece during electroplating, and adapted fordiverting a portion of ionic current from an edge region of the workpiece. In one embodiment, the second auxiliary cathode is locatedperipheral to the work piece holder and radially outward of a peripheralgap between the ionically resistive ionically permeable element and thework piece holder. In one embodiment, the (first) auxiliary cathode is avirtual auxiliary cathode having an associated physical cathode housedin a cavity in a plating chamber, wherein the cavity is in ioniccommunication with the plating chamber. Electroplating apparatus mayfurther include a second ionically resistive ionically permeableelement, wherein the second ionically resistive element is positionedproximate the auxiliary cathode. These features will be discussed inmore detail below, in relation to the associated drawings.

FIG. 1 depicts cross section schematics of an electroplating apparatus,100, at the start of plating and after having plated a number of workpieces. Apparatus 100 includes a plating cell, 105, which has aconsumable anode, 110. In this example, the work piece is asemiconductor wafer, 120 a, which is held by a wafer holder, 115. Anelectrolyte, 125, is used to carry charge between the wafer and theanode, across a distance A, and electroplate metal ions from consumableanode 110 onto wafer 120 a. The right portion of FIG. 1, shows apparatus100, after a number of wafers have been processed in the system. In thisexample, wafer 120 z is being plated. Anode 110 has been partiallyconsumed and the distance between the wafer and the anode is now larger,distance B. As mentioned, this change in distance corresponds to achange in resistivity and a corresponding change in uniformity of platedmetal onto the wafers being plated in the apparatus.

One could conceivably change the (vertical) position of the wafer tomaintain the gap between the wafer and the anode surface; however, it istypically the case where the conditions at and around the wafer surfaceare carefully controlled during plating. For example, auxiliary cathodesand resistive elements are also used to shape the field near the wafersurface to aid in uniform plating. Thus, essentially, as the anode isconsumed it is moving away from the carefully controlled environment atand around the wafer. Moving the wafer would disturb this environmentand make maintaining the carefully configured field more difficult. Theinventors realized that since the anode is essentially moving away fromthis carefully configured local environment as it is consumed, it wouldbe beneficial to develop technology that would allow the anode's platingsurface to stay positioned substantially as when plating started as itis consumed, so that the gap between the wafer and the anode ismaintained.

FIG. 2, depicts plating apparatus 100, with an anode support, 130, asdescribed herein. Anode support 130 includes a positioning mechanism(not shown) which positions the anode during plating so that the optimaldistance, A, is maintained throughout plating. In this example thedistance is maintained from plating onto wafer 120 a to wafer 120 z,even though a significant portion of anode 110 has been consumed. FIGS.3A-5E show more detailed examples of apparatus incorporating such anodesupports. Anode positioning mechanisms include components for applying aforce, in many instances and upward force, against the consumable anodein order to maintain the gap between the anode and the work piece. Thisforce may be supplied by, for example, hydraulics, springs, screwdrives, and the like.

FIG. 3A shows a perspective of an anode assembly, 300, which includes ananode support which includes base plate, 310, charge plate, 315 andsupport plate, 340. Assembly 300 resides in a plating cell (depicted inFIGS. 3B and 3C) during plating. On base plate 310 are a series ofsprings 325. In this example, springs 325 have elastomeric boots, 335,that envelope the springs and protect them from the corrosiveelectrolyte during plating. Base plate 310 also includes a series ofguide rods, 330, each located in the center of a spring 325. Boots 335can slidably engage guide rods 330, that is, when springs 325 arecompressed, the boots slide down the guide rods and form a seal so thatelectrolyte doesn't come in contact with the springs. Charge plate 315is connected to base plate 310 via cables 320. Cables 320 are used tocarry current to the charge plate from a power source (not shown). Inone embodiment, cables 320 are titanium. In another embodiment, chargeplate 315 is also titanium. Base plate 310 may also be titanium. In oneembodiment, cables 320 are affixed to base plate 310 via crimp tubes(see for example FIG. 5A) that are welded onto base plate 310. Cables320 may also be, for example, bolted to the base plate and/or the chargeplate. In one embodiment, the springs may be coated with a polymericmaterial that protects them, with or without boots as described. In oneembodiment, the polymeric material is Teflon. In one embodiment, thesprings are stainless steel.

Support plate 340 has a hollow, 345, which suitable for charge plate 315to pass through. In this example, the support plate also includesrecesses, 350, which accommodate tabs on the perimeter of charge plate340 to in order to engage and register the charge plate with the supportplate. Support plate 340 also has one or more protrusions, 355, whichengage with recesses 375 on the anode. In this example, protrusions 355also have apertures which allow guide posts 330 to pass through when thesupport plate is resting on and compressing springs 325. One of ordinaryskill in the art would appreciate that springs 325, that lift supportplate 340, need not necessarily rest against a base plate, but couldrest against a bottom region of a plating cell, or both. Referring toFIG. 3B, in this example, depression 375 a registers with protrusion 355a on support plate 340, while depressions 375 b, register withprotrusions 355 b on the support plate. Thus alternating anode sectors,365, register with one or two protrusions on the support plate,respectively.

In this example, the consumable anode, 360, includes four sections,which are circular sectors, 365, having 90° central angles. Anodes ofthe invention are not limited to this configuration, they may have aunitary body, or more or less sections, for example, two half-circlesthat register to make a disk shaped anode, three circular sectors with120° central angles, etc. Each sector 365 has a number of throughchannels. In this example, through channels, 380, are used to passfasteners, for example bolts, down through the channels and fasten theanode sectors to the charge plate. Anode sectors 365 also have throughchannels, 370, which allow guide rods 330 to pass through them when theanode is resting on support plate 340 and springs 325 are at leastpartially compressed. Anode sectors 365 also have depressions, 375,which register with protrusions 355 on support plate 340 when the anodeis positioned on the support plate. Collectively, springs 325 havesufficient strength to lift anode 360 from their compressed state totheir extended state.

Referring to FIG. 3B, which depicts assembly 300 as well as a platingcell, 305, in order to assemble apparatus 300, charge plate 315 isbrought through hollow 345 in support plate 340. Cables 320 aresufficiently long so as to allow charge plate to pass through thehollow, at least when springs 325 are compressed. In this example,charge plate 315 is rotated (as indicated by the heavy dashed arrow) inorder to register its perimeter tabs with depressions 350. In thisexample, when registered with support plate 340, the charge plate issubstantially in the same plane as support plate 340. In one embodiment,cables 320 are configured such that springs 325 must be compressed, forexample by applying downward force to the support plate against thesprings, in order for the charge plate to pass through the hollow in thecharge plate. Once the charge plate's perimeter tabs are registered withdepressions 350 in the support plate, the downward force against thesupport plate is ceased and the support plate pushes up against thecharge plate via the depressions 350 pushing upwards on the perimetertabs. In this way, a unitary support assembly is made from the supportplate and the charge plate. Anode sectors 365 are bolted to the chargeplate (in some embodiments the anode sectors are also fastened to eachother, infra). The support assembly holds the anode such that springs325 are extended. Then the anode, charge plate and support plate arecollectively pushed downward in order to compress springs 325. In thisexample, plating cell 305 has a hollow for accommodating anode assembly300.

While the anode assembly is compressed in the hollow of plating cell305, a hard stop, 385, in this example having an annular structure withspokes, 390, is fastened to the top of the hollow in cell 305, in orderto hold anode 360 in place, against the force of springs 325 which pushupwardly against the hard stop. FIG. 3C depicts the hard stop in place,holding the anode down in the hollow of plating cell 305. Using thisassembly, during plating, as the surface of anode 360 is consumed, theforce supplied by springs 325 keeps the anode pressed against hard stop385. During plating, a wafer holder (not shown) holds a wafer at a fixedlevel (indicated by the dotted line) above the anode. As the anode isconsumed, distance A is maintained. Thus the term “front referencedanode” may be used to describe how the anode's “front” face isreferenced so that it stays in the same position during plating.

The particular configuration of the apparatus in FIGS. 3A-C is oneembodiment of an anode assembly and does not limit the scope of theinvention. Further, the apparatus described herein can be used with avariety of plating cells. Such plating cells may include one or morefeatures including field shaping elements, auxiliary cathodes,semi-permeable membranes for defining separate anode and cathodechambers, and the like. Such features are exemplified in U.S. patentapplication Ser. No. 12/481,503, filed Jun. 9, 2009, titled, “Method andApparatus for Electroplating,” naming Steven T. Mayer, et. al. asinventors, which is hereby incorporated by reference herein for allpurposes. FIG. 4 describes one such cell generically, so as to providecontext to subsequent description herein.

FIG. 4 shows a schematic cross section of an exemplary electroplatingapparatus, 400, in which the anode assemblies described herein may beemployed. For the sake of clarity, the anode assembly components, forexample anode support and positioning mechanism are not shown in FIG. 4,but are described in further detail with respect to an exemplary platingapparatus described in relation to FIGS. 5A-5F.

Electroplating system 400 includes an electroplating chamber thatcontains an anode chamber and a cathode chamber. The anode chamberincludes two chambers, a “lower” anode chamber including a separatedanolyte chamber (SAC) 402 where the anode assembly (including anode 110and anode support 130 which includes an anode positioning mechanism asdescribed herein) resides, and an upper diffusion chamber 404 (alsoreferred to as a HRVA chamber or a catholyte chamber), separated fromthe separated anolyte chamber by a cationic membrane 408. The diffusionchamber contains a highly resistive ionically permeable element(sometimes referred to as a highly resistive virtual anode, or HRVA)410, described above, and an electrolyte solution (sometimes referred toas the catholyte), which is shown at a level 412. The separated anolytechamber also contains an electrolyte solution (sometimes referred to asthe anolyte), which may or may not be the same type of electrolyte inthe diffusion chamber.

The HRVA 410 is located in close proximity (within 10 mm, preferablywithin 5 mm) of a wafer, 414, and serves as a high resistance ioniccurrent source to the wafer. The element contains a plurality of 1Dthrough channels and is described in detail in U.S. patent applicationSer. No. 12/481,503, incorporated by reference above.

Wafer 414 is held and positioned by wafer holder 416, and immersed inthe electrolyte solution (i.e., the catholyte). In some embodiments, thewafer holder 416 is a clamshell apparatus which makes contacts to theperiphery of the wafer through a number of contact fingers housed behinda typically elastic “lip seal”, which serves to seal the clamshell andkeep the edge contact region and wafer backside substantially free ofelectrolyte, as well as to avoid any plating onto the contacts. Ageneral description of a clamshell-type plating apparatus having aspectssuitable for use with this invention is described in detail in U.S. Pat.No. 6,156,167 issued to Patton et al., and U.S. Pat. No. 6,800,187issued to Reid et al., which are both incorporated herein by referencefor all purposes.

Cationic membrane 408 allows ionic communication between the separatedanolyte chamber and the diffusion chamber, while preventing theparticles generated at the anode from entering the proximity of thewafer and contaminating it. The cationic membrane is also useful inprohibiting non-ionic and anionic species such as bath additives frompassing though the membrane and being degraded at the anode surface, andto a lesser extent in redistributing current flow during the platingprocess and thereby improving the plating uniformity. Detaileddescriptions of suitable ionic membranes are provided in the followingUS patents and patent applications: U.S. Pat. Nos. 6,126,798 and6,569,299 issued to Reid et al., U.S. patent application Ser. No.12/337,147, entitled Electroplating Apparatus With Vented ElectrolyteManifold, filed Dec. 17, 2008, U.S. Patent Application Ser. No.61/139,178, entitled PLATING METHOD AND APPARATUS WITH MULTIPLEINTERNALLY IRRIGATED CHAMBERS, filed Dec. 19, 2008, each of which isincorporated herein by reference for all purposes.

Electrolyte solutions are continuously provided to the separated anolytechamber and the diffusion chamber by separate pumps (not shown). For thediffusion chamber, electrolyte enters the chamber through a manifold(not shown) and exits by flowing over weir wall 418.

Electroplating apparatus 400 also contains an auxiliary cathode 420 anda second auxiliary cathode 422. In the depicted embodiment, auxiliarycathode 420 and second auxiliary cathode 422 are virtual cathodes, withassociated physical cathodes (not shown). In other embodiments, one orboth of the virtual cathodes are replaced by physical cathodes, and thephysical cathode is simply located at the position of the virtualcathode. The electroplating apparatus performs in a similar manner witheither virtual cathodes or physical cathodes (with no virtual cathodes).The use of virtual cathodes provides advantages, however. Furtherdescription of the cathodes, HRVA, anode and their interrelationship isdescribed in detail in U.S. patent application Ser. No. 12/481,503,incorporated by reference above.

Thus, apparatus 400 includes an ionically resistive ionically permeableelement located in close proximity of the wafer and at least oneauxiliary cathode located between the anode and the ionically resistiveionically permeable element. The ionically resistive ionically permeableelement serves to modulate ionic current at the wafer surface. Theauxiliary cathode is configured to shape the current distribution fromthe anode. The configuration effectively redistributes ionic current inthe plating system allowing plating of uniform metal layers andmitigating the terminal effect. Anode support 130 maintains a consistentgap between the plating surface of wafer 414 and the consumed surface ofthe anode 110, as described herein. This aids in uniform plating bymaintaining a substantially constant field configuration between thewafer and the anode, because, among other things, the gap does notchange during plating.

FIGS. 5A-F depict aspects of a plating apparatus which incorporatesanode assemblies as described herein. FIG. 5A depicts an assembly, 500,which includes a plating cell, 505, and analogous components to thosedescribed in relation to FIGS. 3A-C, but with some differences. Baseplate, 510, is connected to charge plate, 515, via cables, 520. Springs525 (see FIG. 5B) reside inside boots, 535. The top of guide rods, 530,can be seen protruding through apertures in protrusions, 555, on supportplate 540. In FIG. 5A, charge plate 515 is engaged with support plate,540. Referring to FIG. 5C, the hollow, 545, in support plate 540 isrectangular. Depressions, 550, engage with perimeter tabs, 551, ofcharge plate 515. In this example, in order to engage the charge plateand the support plate, the anode assembly is compressed as describedabove, and charge plate 515 is passed through hollow 545. In thisexample, charge plate 515 need not also be rotated, but rather, when itis brought through hollow 545 it is tilted out of plane of support plate540 (when in plane with support plate 540, charge plate 515 will notpass through hollow 545). Once the charge plate is entirely throughhollow 545, the charge plates is brought parallel to the plane of thesupport plate and the support plate is allowed to rise by the force ofthe springs. This engages the support plate with the charge plate asdepicted in FIG. 5A. In this example, cables 520 limit charge plate 515from traveling (vertically) past the full extension of springs 525. Thismeans that when the springs press against support plate 540, depressions550 engage perimeter tabs 551 and the support plate is prevented fromtraveling (vertically) past the charge plate. Note that guide rods 530protrude from the apertures in protrusions 555 in this configuration(see FIG. 5A); this aids in registration of the assembled anode sectorswith the support plate. Note also that protrusions 555 havecorresponding depressions under support plate 540. The top of springs525 seat in these depressions (see FIG. 5B).

In this example, anode sectors 565 are fastened together and bolted tocharge plate 515. Referring to FIGS. 5D-E, the top (as depicted in FIG.5D) surface of each anode sector has a substantially planar surface,although there are, for example, apertures as described for passingguide rods 530 and fasteners through as described in relation to FIGS.3A-C. Anodes described herein may have local deviations from planaritysuch as ridges, depressions and the like. Based on modeling and actualplating performance, it is expected that plated film thickness profilewill not show obvious change when topography of the front surface of theanode varies by between about 5 mm and about 10 mm. Thus it, localdeviations from planarity will not change the plating uniformityperformance unless the deviation is greater than about 10 mm. In oneembodiment, the top surface of the consumable anode has a topographythat varies no more than 10 mm in height on average. Referring to FIGS.5D-E, channels in the anode segments for bolting the anode segments tothe charge plate are deeper than 10 mm. However, these deviations inheight beyond 10 mm are localized and do not affect plating uniformityfor two reasons: 1) because the wafer is typically rotating duringplating, any changes in the field produced by the holes (null field) isaveraged from the perspective of the rotating wafer, and 2) because thegap between the anode and the wafer is on the order of inches, the fieldaround the holes confluences at a distance above the holes so that theoverall effect of these localized deviations in height do not translateinto plating non-uniformity. In one embodiment, these holes are occupiedwith copper plugs to compensate for any variation in the field.

FIG. 5D also shows the bottom surface of each anode sector, 565.Depressions, 575, in this example circular depressions, register withprotrusions 555 on support plate 540, when the anode is engaged withsupport plate 540. Referring to FIG. 5E, connectors, 501 and 502, arefastened to two each of the anode sectors 565. Two anode sectors, havingconnector 501 fastened thereto, are placed onto the charge plateopposite each other, for example as sectors 565 a and 565 b arepositioned in FIG. 5A. The portion of connector 501 that overhangs eachof the two anode sectors is used to support the remaining two sectors,each bearing connector 502. Since connector 502 has no overhang, theseanode sectors can be slid downward and into the space between anodesectors 565 a and 565 b. Fasteners, for example bolts or screws, areintroduced into through channels, 580, and they pass through anaperture, 503, in connector 502 and aperture, 504, in the overhangportion of connector 501, and fasten to charge plate 515. In this way,the anode sectors are fastened to each other and to charge plate 515.

In this example a hard stop, 585, is configured as a spoked wheel. Inthis example, the individual spokes, or flutes, 590, are hollow forflowing electrolyte therethrough, and have apertures (not shown) whichflow electrolyte onto the anode surface during plating to aid inpreventing passivation of the anode surface. Hard stop 585 hasprotrusions, in this case configured as “bumps,” 595, (see also FIGS. 5Band 5F) that rest against the surface of the anode during plating, thusminimizing physical contact between the hard stop and the anode. Thisconfiguration also allows flutes 590 to have apertures on their surfaceproximate to the anode surface, and thus electrolyte can flow moreefficiently to the surface of the anode during plating to help preventpassivation. Referring to FIG. 5B, which shows the anode assembly insideplating chamber 505, hard stop 585 is depicted fastened to the platingchamber and holding down the anode sectors 365. Also included in thiscell is a membrane, 596, for example as described in relation to FIG. 4,which creates a lower anode chamber housing the anode, and betweenmembrane 596 (membrane support structure indicated) and a HRVA, 597, isthe upper anode chamber. A wafer holder (not shown) positions the wafer(not shown) at a fixed height (as indicated by the dashed line), andthus the gap, A, between the anode and the wafer is established. Duringplating, as the anode is consumed, the anode support, via itspositioning mechanism, maintains gap distance A. One embodiment is ananode assembly, and/or components thereof, as described herein.

Another embodiment is a method of electroplating a metal onto a workpiece, the method including maintaining a consistent distance betweenthe plating surface of the work piece and a surface of a consumableanode during plating, by adjusting the position of the consumable anodeduring plating to compensate for consumption of the surface of theconsumable anode. FIG. 6 depicts aspects of a process flow, 600,outlining such methods. Referring to FIG. 6, a work piece is positionedin a plating cell, see 605. Then plating is started, the platingemploying a consumable anode, see 610. During plating, the gap betweenthe work piece and the anode are maintained, see 615, then the processflow is complete. In one embodiment, the consistent distance between theanode and work piece varies during plating by no more than about 10 μm,in another embodiment, no more than about 5 μm, in another embodiment,no more than about 2 μm. When plating, for example, 300 mmsemi-conductor wafers with copper, using an anode (segmented or not)that weighs on the order of 30-40 kg, the anode thickness changes verylittle during each wafer plating (in range of 1 μm to 1.5 μm). However,by maintaining a consistent distance during plating, continuous tooloperation times are increased without sacrificing uniformity. Forexample, in conventional plating tools, an anode might be on the orderof 3 cm to 4 cm thick. Typically the anode would not be made thicker,because the gap increases over time, due to the anode being consumed;gap changes larger than about 2 or 3 cm would bring platingnon-uniformity into unacceptable ranges. In applications demandinghigher plating uniformity, even this conventional gap change isunacceptable. Using methods and apparatus of the invention, anodes canbe, for example, 10 cm thick (or more) and about 90% or more of theanode can be used without changing the gap and therefore high platinguniformity is maintained. Theoretically, all of the anode could be used,the current limitations being related only to existing hardware used tomount the anode, for example screws holding the anode to the chargeplate, interfering with the localized field. In one embodiment, thislimitation is overcome by appropriate mounting of the anode so thatnearly all of the anode can be used without sacrificing uniformity. Toput this example in perspective, using methods and apparatus of theinvention, an anode that is on the order of 10 cm thick (for plating on300 mm wafers) that weighs on the order of 30-40 kg, can be used formonths to plate tens of thousands of wafers while maintaining aconsistent gap and therefore without sacrificing plating uniformity.

In one embodiment, the work piece is a semiconductor wafer. In certainembodiments, the surface of the consumable anode comprises asubstantially planar surface that is substantially parallel to theplating surface of the semiconductor wafer during plating. In someembodiments, the substantially planar surface is at least co-extensivewith the plating surface of the semiconductor wafer.

In certain embodiments, apparatus as described herein are used toimplement the methods described. Copper electroplating is employed incertain embodiments. In certain embodiments, apparatus include platingchambers as described herein and in the incorporated references. Forexample, in one embodiment, the work piece and the consumable anode areprovided in a plating chamber including: (i) an ionically resistiveionically permeable element located between the work piece and theconsumable anode during plating, the ionically resistive ionicallypermeable element having a flat surface that is substantially parallelto and separated from the plating surface of the work piece by a gap ofabout 5 millimeters or less during electroplating; and (ii) an auxiliarycathode located between the consumable anode and the ionically resistiveionically permeable element during plating, the auxiliary cathodeperipherally oriented to shape the current distribution from theconsumable anode, while the auxiliary cathode is supplied with currentduring electroplating. In one embodiment, the ionically resistiveionically permeable element has an ionically resistive body with aplurality of non-communicating channels through the body, where saidplurality of non-communicating channels allow for transport of ionsthrough the element, and wherein substantially all channels have aprincipal dimension or a diameter of the opening on the surface of theelement facing the surface of the work piece of no greater than about 5millimeters. In certain embodiments, the ionically resistive ionicallypermeable element is a disk having between about 6,000-12,000 channelsand/or has a porosity of about 5% porous or less. Some embodimentsfurther include positioning a second auxiliary cathode in substantiallythe same plane as the plating surface of the work piece duringelectroplating, and said secondary auxiliary cathode adapted fordiverting a portion of ionic current from an edge region of the workpiece. In one embodiment, the second auxiliary cathode is locatedperipheral to the work piece holder and radially outward of a peripheralgap between the ionically resistive ionically permeable element and thework piece holder. In some embodiments, the auxiliary cathode is avirtual auxiliary cathode having an associated physical cathode housedin a cavity in the plating chamber, where the cavity is in ioniccommunication with the plating chamber. In certain embodiments, methodsdescribed herein further include positioning a second ionicallyresistive ionically permeable element proximate the auxiliary cathodeduring plating.

Although the foregoing invention has been described in some detail tofacilitate understanding, the described embodiments are to be consideredillustrative and not limiting. It will be apparent to one of ordinaryskill in the art that certain changes and modifications can be practicedwithin the scope of the appended claims.

We claim:
 1. An electroplating apparatus, comprising: (a) a work pieceholder for holding a work piece in place during electroplating; and (b)an anode support comprising an anode positioning mechanism for adjustingthe position of a consumable anode to provide a consistent distancebetween the consumable anode and the work piece over a period of timeduring which the consumable anode is consumed.
 2. The apparatus of claim1, wherein the work piece holder is configured to hold a semiconductorwafer.
 3. The apparatus of claim 2, further comprising the consumableanode, wherein the consumable anode comprises a substantially planarsurface that is substantially parallel to the plating surface of thesemiconductor wafer during plating.
 4. The apparatus of claim 3, whereinthe substantially planar surface is at least co-extensive with theplating surface of the semiconductor wafer.
 5. The apparatus of claim 1,wherein the consumable anode comprises two or more sections that, whenregistered with each other, form a disk-shaped anode.
 6. The apparatusof claim 5, wherein the consumable anode comprises four circular sectorshaving equivalent central angles.
 7. The apparatus of claim 1, whereinthe anode positioning mechanism comprises: (i) a support plate, forsupporting the consumable anode; and (ii) a drive component, configuredto apply upward force to the support plate sufficient to raise theanode.
 8. The apparatus of claim 7, wherein the drive componentcomprises one or more springs that are compressed between the supportplate and a bottom region of a plating chamber and/or a base plateconfigured to lie in the bottom region of the plating chamber.
 9. Theapparatus of claim 8, wherein the one or more springs are compressedbetween the support plate and the base plate.
 10. The apparatus of claim8, wherein the anode positioning mechanism further comprises a hard stopconfigured to limit the distance that the consumable anode is pushed bysaid one or more springs and thereby maintain said consistent distancebetween the consumable anode and the work piece over said period of timeduring which the consumable anode is consumed.
 11. The apparatus ofclaim 10, wherein the hard stop comprises an annular structure.
 12. Theapparatus of claim 7, wherein the support plate is annular with a hollowoccupied by a charge plate, said charge plate configured attach to thebottom of the consumable anode and attach to the base plate via one ormore cables.
 13. The apparatus of claim 1, wherein the consumable anodecomprises copper.
 14. The apparatus of claim 1, further comprising: (i)an ionically resistive ionically permeable element shaped and configuredto be positioned between the work piece and the consumable anode duringelectroplating, the ionically resistive ionically permeable elementhaving a flat surface that is substantially parallel to and separatedfrom a plating face of the work piece by a gap of about 5 millimeters orless during electroplating; and (ii) an auxiliary cathode locatedbetween the consumable anode and the ionically resistive ionicallypermeable element, and peripherally oriented to shape the currentdistribution from the consumable anode, while the auxiliary cathode issupplied with current during electroplating.
 15. A method ofelectroplating a metal onto a work piece, the method comprisingmaintaining a consistent distance between the plating surface of thework piece and a surface of a consumable anode during plating, byadjusting the position of the consumable anode during plating tocompensate for consumption of said surface of the consumable anode. 16.The method of claim 15, wherein the consistent distance varies duringplating by no more than 10 μm.
 17. The method of claim 16, wherein thework piece is a semiconductor wafer.
 18. The method of claim 17, whereinpositioning the consumable anode during plating comprises employing ananode positioning mechanism which comprises: (i) a support plate, forsupporting the consumable anode; and (ii) a drive component, configuredto apply upward force to the support plate sufficient to raise theanode.
 19. The method of claim 18, wherein the drive component comprisesone or more springs that are compressed between the support plate and abottom region of a plating chamber and/or a base plate configured to liein the bottom region of the plating chamber.
 20. The method of claim 19,wherein the anode positioning mechanism further comprises a hard stopconfigured to prevent the consumable anode from being pushed by said oneor more springs and thereby maintain said consistent distance.